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Seven Questions for Quantum Physicists

  1. Sep 20, 2008 #1
    I am interested in the irrational. I have the usual layman's understanding of the double-slit experiment, which I am told is the cornerstone of quantum irrationality. I have a question to clear up my understanding of this, and a few more questions about irrationality in physics.

    You will soon see that I am not a scientist or expert. My grasp of scientific nomenclature is weak at best, and I have quite a naive understanding of modern scientific discoveries. Please, if you reply, can you assume you are talking to a bright GCSE teenager rather than a professor of differential calculus.

    1. The double slit experiment works with matter or light, right? What are the "particles" ("quanta"?) that are fired at the slits?

    2. The particles "know" when they are being measured, right? They are behaving like waves, going through both slits, and then when they are measured they suddenly only go through on slit, right?

    3. What the double-slit experiment must "mean" is that the elementary particles of light / matter are behaving in a way that the brain cannot adequately imagine, in the same kind of way that the brain cannot imagine a line infinitely long, or an object that must be spun 720 degrees to get back to its original point.

    4. I seem to remember reading of a particle like this, that has to be spun twice to get back to the start. Is this right?

    5. What other unimaginable or irrational things happen in the quantum world? Can someone give me, or point me towards a nice little list of things that happen that don't make sense, or rather that can't make sense because they are paradoxical or somehow infinite?

    6. Like I say, I am very interested in the relationship between infinity, paradox and the unimaginable. Anything that anyone has to say that might open up new explorations of these themes would be welcome. I'm not interested in "psuedoscience" or religion (at least abrahamic religion), rather aesthetics and the nature of perception.

    7. Finally, on a completely different topic, probably not physics at all, I recently read that "systems theorists have shown that natural systems and organisms have an innate tendency to move towards complexity, creating a structures which are more than the sum of parts. Apparent order and complexity are not created by genetic mutations, but by the innate emergent properties of matter." Is this so? Where can I read more about this?

    Thank you for your time.
  2. jcsd
  3. Sep 20, 2008 #2


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    Given that you are interested in the irrational, the paradox and the unimaginable, what do you hope one can give you as an answer ?

    It's because of the spaghetti monster. 42, remember ? Never sneeze. In Tartiflette we trust.

    (is that irrational enough ? I'm trying...)

    Seriously, science is about trying to get a more or less rational (even if totally strange) picture of nature. Don't confuse bizarre, weird, strange, unintuitive with irrational, paradoxial, unimaginable. The first are contradictions with our "intuition" and our "common sense" - the second are contradictions with intellectual activity. In as much as science can accept, and often leads to, the first kind of sensations, it can only do so because it tries to avoid at all price the second. If you're interested in the second, we can't help. At all.
  4. Sep 20, 2008 #3
    I realise that few scientists would accept that there is much in reality that is irrational, paradoxical, unimaginable, infinite, eternal and so forth; but are you saying then that such things have no place in science? I understand the results of the double-slit experiment to be paradoxical. Perhaps the first experimenters in this field "avoided" the paradoxical "at all price," but they seemed to have found it. Perhaps if scientists didn't avoid such things at all costs they would make more interesting discoveries?
  5. Sep 20, 2008 #4

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    I see. You aren't a scientist yourself, but scientists are doing it all wrong.
  6. Sep 20, 2008 #5
    I didn't say "they are doing it all wrong", but even if I was, the fact that I am not a scientist does not necessarily make such a claim less worthwhile, useful, true or interesting.
  7. Sep 20, 2008 #6


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    Yes, it does. You have no way of knowing if what you say is true, much less any way to prove it. All you have is a feeling of discomfort about science, combined with a pretty high level of ignorance about it*. And it is self-evident: when you don't understand the rational basis for something, you are likely to find it irrational. The solution would seem obvious: learn about science, and maybe your discomfort with it will go away via understanding. To see that science is rational, you have to learn and understand the rational basis of it.

    *And oh, by the way: science has worked better than any other method of attempting to understand how the universe works. Hands down. The period just before science was invented was called "The Dark Ages" for good reason. So it is a little arrogant to believe that out of your ignorance can come a superior method for approaching understanding of the universe.
    Last edited: Sep 20, 2008
  8. Sep 20, 2008 #7


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    The problem with most of your "irrational" things is that they're nowadays considered old hat. I still consider the "infinitesimal" of Newton and Leibniz worse than anything in quantum mechanics (the mathematicians have thrown it away, but I think most physicists still use it).

    What are the most far-out things that are still considered "respectable science"?

    http://www.quiprocone.org/Protected/DD_lectures.htm (This one is probably not weird enough for you)
  9. Sep 20, 2008 #8
    I'm not quite sure what I have said that warrants such a hostile tone. Please note that I am not saying much here; and so its truth or falsehood is moot. I am asking questions. If you have answers, please give them to me, if my questions are foolish, please point out why.

    I did say "the fact that I am not a scientist does not necessarily make such a claim less worthwhile, useful, true or interesting." Which I hold to. There is nothing to say that a non-scientist cannot point out a scientist's error. This is not what I am doing here though.

    You are right that I have "a high level of ignorance" about science. There is a lot of science out there though, isn't there? I've read a few "popular science" books, but that's not saying much.

    I'm not uncomfortable about science though. Honest.

    Perhaps there is a semantic problem here. When I say "irrational" I mean that what the double-slit experiment seems to mean cannot be thought about or imagined; in the same way as infinity cannot be thought about or imagined. A symbol can represent infinity or paradox, and we can think about that, but actual infinity cannot be experienced by finite machinery. That's what I mean when I say infinity and paradox and what the double-slit experiment means are irrational. Perhaps I should use a different word though.

    (I do believe that infinity and paradox can be experienced, by the way, just not with the mind; with something more intelligent)

    You seem to be reading quite a lot into my few words.

    Anyrate, the dark ages have this name, as far as I know, because we know very little about what happened during them, not because they were a time of darkness. They almost certainly were a time of darkness, but then the so-called "enlightenment" was hardly a time of peace, cooperation and tolerance. Also the thirteenth century saw some of the greatest architecture Europe has seen and the appearance of transcendent personal romantic love as something to value and strive towards.

    As far as I know the greatest period of human history that we have any (albeit indirect) record of was between six and twelve thousand years ago; very little warfare, non-hierarchical societies, not much disease. This period definitely preceded science I'd say. Also there have been more than a couple "primitive" tribes, completely ignorant of science, who have displayed far great social intelligence, cooperation and creativity than our "scientific" (if that's what it is) world has yet come up with.
    Last edited: Sep 20, 2008
  10. Sep 20, 2008 #9
    atyy - thanks for the links, very interesting; but I'm not so much in the market for weird theories as weird discoveries and observations (like this double-slit business). I'd really like to know about particles that seem to telepathically understand each other and that simultaneously appear and disappear and all that stuff.
  11. Sep 20, 2008 #10


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    Don't anthropomorphize. When you measure which slit they go through you change the experimental set up so it shouldn't be terribly surprising that you change the experimental result. It doesn't imply any sentience to particles.

    It might mean that it behaves in a way that you cannot adequately imagine today. But since it can be adequately described by math and since math is a construct of the human imagination that is only a question of time and your desire to really learn.

    Since you are talking about a list of things that don't make sense to you or that you cannot imagine then you are the only one who can generate such a list. QM has a solid mathematical framework, so although it may be strange to you it is perfectly logical.
  12. Sep 20, 2008 #11
    Here I am not anthropomorphising. This is why I put "know" between speech marks.

    I didn't know the experimental set-up was so radically changed. Are you saying that the bizarre results of the double-slit experiment are just down to this?

    Adequately described is not the same as experiencing. As far as I know the thinking rational 'scientific' brain can experience dichotomy, discrete information and so forth, but can no more experience non-discrete continuous qualitative information than my nipples can fire laser beams.

    I'm pretty confident that the part of the brain that does maths will never be able to experience infinity and paradox.
    Were it so! Alas I do not have access to electron microscopes, large hadron colliders, oscillating hyper-static ion-chambers, and the like. Nor do I have the kind of knowledge and aptitude for understanding the reports of those that do. I was hoping to get a few crumbs from the table here.
  13. Sep 20, 2008 #12


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    The key words to search for are probably: EPR Paradox, Bell's theorem, Aspect Experiment. You can also search for quantum teleportation, but it's not as weird as it sounds.

    Bell's Theorem

    An experimental test of non-local realism
    Simon Groeblacher, Tomasz Paterek, Rainer Kaltenbaek, Caslav Brukner, Marek Zukowski, Markus Aspelmeyer, Anton Zeilinger

    Experimental test of nonlocal realistic theories without the rotational symmetry assumption
    Tomasz Paterek, Alessandro Fedrizzi, Simon Groeblacher, Thomas Jennewein, Marek Zukowski, Markus Aspelmeyer, Anton Zeilinger

    The Free Will Theorem
    John Conway, Simon Kochen

    The Strong Free Will Theorem
    Authors: John Conway, Simon Kochen
    Last edited: Sep 20, 2008
  14. Sep 20, 2008 #13
    Thank you! Just the ticket.
  15. Sep 20, 2008 #14


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    You originally said "imagine", not "experience". If you can describe it you can imagine it (even when you don't want to, e.g. the imagination that your "nipples can fire laser beams" description evoked). What would be the point of imagination if it were limited to experience?

    That said, yes, we are too big to experience the quantum world, but we can imagine it in great detail.

    Simply ask about specific things that interest you without throwing around anti-scientific words like "irrational"; you will get more than crumbs.
  16. Sep 20, 2008 #15
    In this case I'd say imagine and experience are the same (as imagination for the mind is experience). I cannot experience a paradox in my mind and I cannot imagine it either - in the same way I can imagine, say, two pineapples. In the case of both the pineapples and the paradox I am investigating or using a sign or symbol in my head, but in the case of the paradox there seems to be an inherent uncertainty in the relationship between the sign and what it represents.

    That might be bo@!$cks though.

    Somehow I feel my idea of laser-firing nipples and pineapples is of a different order of idea to "infinity" or "paradox". This is what I am investigating. I beg your indulgence - or your silence.

    As far as I know I have asked about specific things that interest me. Atyy gave me some good answers too. I've never considered the word "irrational" to be "anti-scientific" just lying significantly (although not totally) beyond the cast of its net; like love, for example, or creativity.

    But as I say, its a question of semantics. For me, for example, there is a difference between illogical, irrational, insane and wrong. I should have made my terms clearer.
  17. Sep 20, 2008 #16


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    OK, then we can describe/imagine/experience QM. I think that is stretching credulity on the use of the word "experience", but I won't argue the point.

    Science is a method for applying empirical observation and reason towards gaining knowledge. To describe one of the greatest accomplishments of science as "irrational" (without reason) is therefore very antagonistic, which is why I said anti-scientific instead of just unscientific.
  18. Sep 20, 2008 #17
    I agree that the use of "irrational" is having a destructive effect on what you're trying to say. "Irrational" implies that there is not rigorous reasoning behind something, which there is for all accepted physics. Perhaps the word you are looking for is "counter-intuitive"?

    Unfortunately, most all physics developed in the past hundred or so years is counter-intuitive. Part of the reason for this is that physics has been exploring regimes that are outside of the world we can normally observe, where intuition really has no place.

    The fact that time is relative is often met with rotten vegetables when presented to high school physics students. (How can time progress slower in a fast-moving spacecraft relative to the earth?). BUT, if you accept the fact that light travels at the same speed in all reference frames (which is incontrovertibly true), then a little math proves this time dilation.

    The fact that no one travels fast enough to FEEL the effects of time dilation means your intuition is useless.

    Quantum physics falls into the same category. We like to imagine that we can measure something without affecting it, but that's because we're big dumb animals. You can't measure a length without, for example, observing a constant bombardment of photons reflecting off the object and ruler into our eye. These photons have a small effect on large systems (ones that can be seen with the naked eye...even a speck of dust), but when you're looking at an atom or something of that size, hitting it with a photon is like throwing a wrench into the gears of a machine.

    The grand paradox of quantum physics is that things do not have a definite state until the act of measurement forces it into one. For example, an electron could be spinning one direction or the other, but we don't know (actually, it is spinning in both directions) until measuring it. This is counter-intuitive until you see the rigorous math going into it, the predictions it has made, and that spectacular experiment showing that the act of repeatedly measuring a system will (probabilistically) forbid it from changing states.

    To answer your first question, the particles are usually photons (or electrons).
  19. Sep 20, 2008 #18


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    That's exactly the point I wanted to make in my first post in this thread. There is a mountain of difference (in fact, almost a pure opposition) between "counter-intuitive and weird" on one hand, and "paradoxical and irrational" on the other.

    As you say, most modern physics is counter-intuitive and weird at first (until you get used to it, and then you start getting some "intuition" for it). There are really bizarre things out there. But, and that's important, most of these things have adequate, logical theoretical descriptions - even though they go against about all we think we can feel about nature. It shouldn't surprise us: "intuition" and "familiarity" comes about because of accumulated experience. If you enter in a domain where you don't have any experience, your accumulated experience is not bound to give valid hints. That's what happens.

    However, when one talks about "irrational and paradoxical", then that means: "truth" and "falsehood" have no longer any meaning. Statements are both truth and false. Logical deduction fails (if A is true, and if B is true, then A and B can nevertheless be false). Thinking fails. You saw the red light flash, I saw the green light flash, and when we compare our observations, we agree that there was no light flashing, or something of the kind. If this were somehow common in "science", then it couldn't be counter-intuitive at all, simply because it would not be possible to explore anything beyond the intuitively and commonly "known": no logical deduction, no mathematical calculation would be trustable, given that logic, and hence mathematics, is bound to fail (that's what it means: irrational and paradoxical). We couldn't deduce anything. So we couldn't deduce anything "counter-intuitive". It would be all "gut feeling and amazement".
  20. Sep 21, 2008 #19
    A paradox is irrational.

    This is a paradox: A and B cannot both be true at the same time. A is true. B is true.

    This is (an example of) quantum physics: A photon cannot be both a wave and particle at the same time. A photon is a wave. A photon is a particle.

    Therefore the results of quantum physics are irrational? Please point out the fallacy here. I have am happy to be shown wrong.

    I'm not saying the reasoning (theories, technique, etc) of QP is irrational, but the results (the observations, etc) are. This to me makes sense, as life itself is fundamentally irrational. Not completely irrational; it is partly rational, and that for that part we have science. (scientists err, in my opinion, by using rationality to understand the un-understandable - but I digress).

    Would anyone like to take a stab at answering my questions? I'm quite satisfied with atyy's links, but anything else on this tack would be valued. Thanks for the info about photons icelevistus - are photons and electrons found in light and matter, or is one found in one and another in another, or what?
  21. Sep 21, 2008 #20


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    Well, a photon is neither a (classical) particle, neither a (classical) wave, but its behavior is sometimes similar to that of a (classical) particle, and sometimes similar to that of a (classical) wave, and most of the time, it's different from both. A photon is an excitation of a quantum field.
    It is true that the Copenhagen picture of quantum theory is somewhat paradoxial and irrational, but you're not obliged to adhere to it. There are much cleaner pictures of quantum theory.

    That's what some people claim(ed). It doesn't have to be looked up that way. The "paradoxes" only come about because we want to force upon modern physics certain properties/views which are not compatible with it. If you let these a priori notions go, then the paradoxes go away too.
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